The formation of coal agglomerates from aqueous slurries containing particulate coal and oil has been widely practiced for many years. Many agglomeration processes have been proposed requiring varying degrees of energy input and oil consumption. Most processes having acceptable energy input requirements and residence times produce relatively oily or sticky coal agglomerates which, while being suitable as a feed stock for the immediate production of a coal-oil mixture, have been found to be unsuitable for long-term storage or transportation due to their stickiness and/or poor physical strength.
Examples of prior art agglomeration processes may be found in U.S. Pat. Nos. 4355999 Masologites, 4302211 Verschun and Australian Patent 534563 (AU-B 54496/80) Dudt. In each of the above processes, long residence times and/or multiple agglomeration stages are required to achieve an acceptable coal agglomerate and even then such products are not necessarily suited to transportation in large bulk carriers of the type which would make transportation of such agglomerates economically viable. In the case of AU-B 54496/80, it will be noted that a four stage process of increasing energy input is required to produce an acceptable agglomerate. Although the agglomerates produced by this process would be acceptably dry (that is, not sticky), the agglomerates would be unlikely to be of sufficient quality to survive transportation without unacceptable production of fines during the transportation process.
It is also well known to reduce the oiliness or stickiness of particulate coal agglomerates by the evaporative de-oiling of such agglomerates. However, such processes have the obvious disadvantage of increasing the energy requirements of the production process since super heated steam must usually be produced to provide the necessary energy to cause evaporation of the oil coating the agglomerates.